1. Field of the Invention
The present invention relates to a direct backlight used in display devices and a display device incorporating the backlight.
2. Description of the Related Art
A liquid crystal display device includes a liquid crystal panel for forming images and a backlight for supplying light to the liquid crystal panel. The backlight is largely classified into two types: a direct backlight and an edge lit backlight. The direct backlight includes a plurality of elongated light sources placed behind the liquid crystal panel when viewed from a viewer. The edge lit backlight includes a light guide plate placed behind the liquid crystal panel and an elongated light source placed along an edge of the light guide plate. The direct backlight is configured such that the plurality of elongated light sources are attached to mounts, and a reflector sheet placed behind the elongated light sources to reflect light emitted from the elongated light sources toward the liquid crystal panel. In front of the elongated light sources, i.e., on the liquid crystal panel side, there is provided a diffuser plate for diffusing light emitted from the elongated light sources, thereby uniformly distributing the light across its area. The diffuser plate is typically a white translucent plastic plate. The mounts, the reflector sheet, and the diffuser plate are fixed to a chassis. For example, the chassis is box-shaped and configured to accommodate therein the mounts, the reflector sheet, and the diffuser plate.
Furthermore, for example, as disclosed in Japanese Patent Laid-Open Publications No. Hei 10-326517, No. 2002-116704, and No. 2002-244118, the direct backlight also includes a spacer pin which is erected from the bottom surface of the chassis toward the diffuser plate. The spacer pin is intended to allow its tip to contact with the diffuser plate when the diffuser plate is deflected toward the elongated light sources, thereby restricting the diffuser plate from being further deflected. A relatively small direct backlight has one spacer pin disposed at its center, whereas a relatively large direct backlight has a plurality of spacer pins. In general, the spacer pin is formed of a white resin in the shape of a truncated cone to prevent it from being visually recognized by the viewer.
However, the aforementioned conventional techniques have the following problems. That is, the spacer pin is preferably made as thin as possible to prevent it from being visually recognized by the viewer. However, a spacer pin that is made excessively thin would be broken when the direct backlight is subjected to external forces such as vibrations or shocks. Additionally, when a user carries a display device, the direct backlight may be shaken so that the tip of the spacer pin and the diffuser plate are rubbed against each other, causing abnormal noises to occur.
To enhance the strength of the spacer pin, it may be contemplated to form a metal material into a truncated cone member by cutting, which is then painted on its surface to form the spacer pin. However, this method requires high costs to manufacture the spacer pin and is thus impractical. Furthermore, a thin spacer pin made of metal would raise a problem that its base portion, i.e., the joint portion with the chassis may be easily broken, and the diffuser plate may be whittled when rubbed against the spacer pin.